Iskanje po katalogu digitalne knjižnice

Opis: Today, monoliths are well-accepted chromatographic stationary phases due to several advantageous properties in comparison with conventional chromatographic supports. A number of different types of monoliths have already been described, among them recently a poly(high internal phase emulsion) (PolyHIPE) type of chromatographic monoliths. Due to their particular structure, we investigated the possibility of implementing different mathematical models to predict pressure drop on PolyHIPE monoliths. It was found that the experimental results of pressure drop on PolyHIPE monoliths can best be described by employing the representative unit cell (RUC) model, which was originally derived for the prediction of pressure drop on catalytic foams. Models intended for the description of particulate beds and silica monoliths were not as accurate. The results of this study indicate that the PolyHIPE structure under given experimental condition is, from a hydrodynamic point of view, to some extent similar to foam structures, though any extrapolation of these results may not provide useful predictions of pressure versus flow relations and further experiments are required.
Ključne besede: organic chermistry, polymers, monoliths, PolyHIPE, hydrodynamic properties, pressure drop
Objavljeno v DKUM: 01.06.2012; Ogledov: 2313; Prenosov: 111
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Opis: High pressure vapor-liquid phase equilibrium data (P-T-x-y) for the binary mixtures of organic solvent (ethanol, tetrahydrofuran, o-xylene, m-xylene, p-xylene) with CO2 have been measured at temperatures 313.2, 333.2, 353.2 K and pressures from 1 to 14 MPa using a static-analytic method. For the systemsethanol-CO2 and tetrahydrofuran-CO2, the experimental data at 313.2 and333.2 K are in a good agreement with literature data. The experimental results have been correlated by the Peng-Robinson equation of state in combination with van der Waals one fluid mixing rule with two adjustable parameters.
Ključne besede: chemical processing, high pressure technology, carbon dioxide, ethanol, tetrahydrofuran, xylene, vapor-liquid equilibrium, experimental data, PR equation of state
Objavljeno v DKUM: 01.06.2012; Ogledov: 2869; Prenosov: 125
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Opis: Proteinase from Carica papaya latex was tested on its thermal stability at atmospheric pressure and in supercritical carbon dioxide, near-critical propane and dimethyl-ether. In supercritical carbon dioxide at 300 bar thermalactivation of the examined proteinase was improved in the comparison toatmospheric pressure. In propane and dimethyl-ether (300 bar) activity of the examined proteinase decreased. Influence of compressionžexpansion cycles on residual activity of the same proteinase in supercritical carbon dioxide (300 bar and 50 °C) was studied, as well. Different ways of transition from supercritical to low-pressure-state were used which affected residual activityof the proteinase.Addition of water in the system increased activity of proteinase from C. papaya, which was incubated in supercritical carbon dioxide for 24 h. Optimum amount of water was found to be between 0.5 and 0.7 g/L.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, proteinase, thermal stability, pressure stability, enzyme activity, water content, dense gases
Objavljeno v DKUM: 01.06.2012; Ogledov: 2015; Prenosov: 28
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Opis: This paper presents a novel approach to the determination of passive soil pressures: using the upper-bound method within the framework of limit analysistheory. It is based on a three-dimensional, kinematically admissible, rotational, hyperbolical failure mechanism. The failure mechanism is composed of the central and two lateral bodies, which are connected by a common velocity field. This approach is similar to two-dimensional stability analyses, where the log spiral potential failure surface is considered. The front surface of the central body interacts with the retaining wallč the uppersurface can be loaded by surcharge loadingč and the log spiral segment defines the curved failure surface of the central part. The cross sections of the lateral bodies are in agreement with the cross section of the central body. On the outer side, they are laterally bounded by a curved and kinematically admissible hyperbolic surface, which is defined by enveloping the hyperbolical half cones and part of the case surface of the leading half cone. The results give values for the passive soil pressure coefficients that are for most cases lower than the values determined by the upper-bound method of limit analysis for a translational failure mechanism, as published in the literature.
Ključne besede: geomechanics, soil-structure interaction, limit analysis, earth pressures, passive pressure, failure surface
Objavljeno v DKUM: 01.06.2012; Ogledov: 1923; Prenosov: 106
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Opis: Sugar fatty acid esters are nonionic surfactants, which are used for personal care products, cosmetic applications, and as emulsifiers for food. In recent years, enzymatic synthesis of sugar fatty acid esters is attracting keen attention as a new manufacturing method for future application. Reaction parameters of lipase-catalyzed synthesis of fructose fatty acid esters in organic solvent were optimized in a batch reactor at atmospheric pressure. Optimum conditions for reaction performed in organic solvent at atmospheric pressure were 10% (wžw of substrates) of lipase from Candida antarctica B, 12.14% (wžw of reaction mixture) of molecular sieves at 60 C, and stirring rate of 600 rpm. Esterification of fructose and palmitic acid was performed insupercritical carbon dioxide with and without addition of cosolvent (organicsolvent) at 60 C. Effect of pressure on enzyme activity was studied.
Ključne besede: chemical processing, high pressure technology, supercritical CO2, esterification, organic solvent, lipase catalysed synthesis, fructose fatty esters, Candida antarctica B, enzyme activity
Objavljeno v DKUM: 01.06.2012; Ogledov: 2400; Prenosov: 186
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